In this study, a new analytical method to calculate the assembly force and separation force of cantilever hook type snap-fit was proposed. Finite element analysis and experimental measurement were performed to verify the new approach. It was found out that the conventional analytical method had a few limitations. The solution was only applicable when the retention face angle was small, and there existed a critical value of retention face angle where separation force unreasonably decreased with increase in deflection. The new approach considered large deflection of retention feature and resultant moment term in addition to the previous method, and the solution was obtained explicitly. The new analytical solution could be applied to large face angles without any divergence, and showed good agreement with finite element analysis results. When the face angle was relatively small, both conventional method and new method showed reasonable results; however, when the angle was large, only the new analytical method showed reasonable results. Experimental investigations of forces during assembly and separation showed that the measured forces were much smaller than the predicted values by analytical methods and finite element analysis. The forces were strongly dependent on the rigidity of the mating part and the magnitude of radius at the edges of beam and mating parts. It was found from experiment that the separation force nonlinearly increased as clearance decreased.

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The behavior of a bellows for an electromagnetic control valve was investigated. The bellows consists of an outer metal bellows, inner spring, and metal caps. The bellows needs to have sensitive and precise motion against external loads and pressure loads in order to control the position of the valve accurately. The spring constant of the inner spring and load-displacement curve of the bellows set were measured using a test machine. The inner spring showed a linear relation between load and displacement. The bellows set showed small stiffness at small displacement, and then the stiffness slightly increased upon subsequent displacement. Based on the measured data, finite element analysis was performed. Axisymmetric conditions were applied, and shell elements were used. The effective material properties of the outer bellows material were extracted. Additional analysis was performed, and the behavior of the bellows was analyzed using the finite element model.